1. Field of the Invention
The present invention relates to sweetener compositions comprising monatin or a salt thereof. More particularly, the present invention relates to a method for preserving monatin or a salt thereof.
2. Discussion of the Background
Monatin is a natural amino acid derivative isolated from the root bark of a native plant (Schlerochiton ilicifolius) of northern Transvaal of South Africa, and its structure has been reported by R. Vleggaar et al to be (2S,4S)-2-amino-4-carboxy-4-hydroxy-5-(3-indolyl)-pentanoic acid ((2S,4S)-4-hydroxy-4-(3-indolylmethyl)-glutamic acid) (R. Vleggaar et al., J. Chem. Soc. Perkin Trans., pp. 3095-3098, (1992)). The synthesis of monatin is described in, for example, ZA 87/4288, ZA 88/4220, U.S. Pat. No. 5,994,559, WO03/045914, WO03/059865, WO03/056026, WO04/067494, WO04/053125, C. W. Holzapfel et al., Synthetic Communications, vol. 24(22), pp. 3197-3211 (1994), K. Nakamura et al., Organic Letters, vol. 2, pp. 2967-2970 (2000), and the like. Monatin is a superior sweetener which is 1400 times sweeter than sugar and contains no calories. It is stable to heat and expected to be applicable to various kinds of food.